This invention relates to an aluminum brazing method and a furnace conducting the method. Herein, the wording of the aluminum brazing means to braze aluminum alloys or aluminum with the same kind of materials or other kind of metals.
An aluminum brazing method has been known according to which aluminum members are brazed in an anti-oxidizing atmosphere by forced-convection heating and radiation heating. Due to the ultilization of forced-convection heating, this conventional brazing method provides relatively high heating efficiency and high productivity as compared with methods in which brazing is performed solely by radiation in a muffle furnace or the like. A problem with this conventional method, however, is that the brazing is adversely affected, for example, by the detrimental gas components (e.g., oxygen gas and steam) adsorbed on the aluminum members to be brazed (hereinafter referred to as the "work-pieces") or the detrimental gas components remaining in the gas constituting the anti-oxidizing atmosphere.
To overcome this problem, a method has been disclosed in JP-B2-57-42420 according to which the aluminum members are efficiently preheated by forced convection and radiation in the anti-oxidizing atmosphere and are then brazed mainly by radiation heating. This arrangement helps to reduce, during brazing, the anti-oxidizing atmosphere-gas flow around the sections to be brazed, thereby reducing the amount of detrimental gas components coming into contact with the sections to be brazed.
Apart from this, there has been proposed a method according to which work-pieces coated with flux are brazed in an anti-oxidizing atmosphere primarily by radiation heating and secondarily by convection heating.
Both the brazing method disclosed in the publication mentioned above and the conventional method described above, in which work-pieces coated with flux are brazed in an anti-oxidizing atmosphere primarily by radiation, have the following problem: since the heating of the work-pieces is effected mainly by radiation, temperature variations may occur between work-pieces and work-piece sections depending upon the configuration and arrangement of the work-pieces. When such a temperature variation occurs, the brazing material does not flow to a sufficient degree at those positions where the requisite temperature rise is hard to effect, resulting in deterioration in brazing quality. This problem is particularly serious in a case where the work-piece has a very complicated configuration or in a case where, for the sake of high productivity, the work-pieces are arranged at high density so as to be collectively brazed.
Such a temperature variation might of course be reduced by heating the work-pieces for a longer time at the requisite brazing temperature. Such an increase in heating time, however, would lead to another problem, for example, of erosion of the aluminum members, i.e., the work-pieces, by the brazing material, resulting in a deterioration in productivity. Further, in the case of work-pieces coated with flux, heating the work-pieces for a long time leads to defective brazing due to evaporation of the flux.
The temperature variation due to radiation might also be reduced by arranging the work-pieces at reduced density. That, however, would lead to deterioration in productivity in proportion to the reduction in the arrangement density.